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Repairing Pietra Dura


#1

A client brought in an exquisite, very old bracelet with pietra dura
inlay all over it. A chunk has come out, plus several individual
tesserae. I could find it in my heart to wish the boss had not
accepted this for repair, but here it is on my desk.

I don’t doubt (too much) my ability to put the available pieces back
in place. The main question (at this point, anyway) is what to use to
cement them back in. It has to be something that takes up very little
space, as there is no question of removing any of the old material
(whatever it is) and reconstructing. At most, I can sand a hair’s
bredth off the glue (?) on the back.

Does anyone have experience with this art form and repairs? All I
can find on line is advice mot to buy damaged pieces because they are
so hard to repair.

Great.
Thanks
Noel


#2

Firstly you need to ask your boss, on what basis has he accepted
this for repair? For example has he given a fixed price? or is it
subject to an estimate from you as to time and materials? Because
doing a one off repair to a unusual object can be either easy or a
bottomless pit as to time.

All most any thing can be repaired or remade if money is no object.

So on a technical level, you need to establish approximately how old
it is. this will then give you a clue as to what adhesives were
available to the original maker. Also you would be quite entitled to
scrape some of the adhesive off the stone pieces and or off the
metal? the bracelet is made from.

If it has come apart on account of the owner bending the bracelet to
change its fit, a no no for any bracelet, then the adhesive will
probably be based on plaster of paris, or calcined lime. Heat a
little of the scrapingsto prove this or not.

I assume you have all the pieces to replace where they came from.

Can you see any adhesive between any of the remaining pieces? if you
can you will need to match the colour of the new to the old.

If you cant then a 2 part epoxy is acceptable as it doesnt set
stone/brittle hard and will last the lifetime of the current owner…

Keep us updated as to progress. a picture would help.

If you master this one then it will be another asset to your skills.

Id have no problems taking on such a repair. Wouldnt be cheap tho!!.
Id set aside a whole morning to it and made sure its as good as new.


#3

Noel,

I did a restoration of a Florentine pietra dura specimen table quite
a few years ago; it’s written up in Lapidary Journal, September,
2003. The original adhesive in that case was something that
heat-softened; if I remember correctly it was pitch or a pitch-like
compound. Keep in mind that this is artisanal work and every maker
may have had his own preferred formulation; short of having access to
a forensic lab you’ll likely not match it exactly.

Cheers,
Hans Durstling
Moncton, Canada


#4
A client brought in an exquisite, very old bracelet with pietra
dura inlay all over it. A chunk has come out, plus several
individual tesserae. I could find it in my heart to wish the boss
had not accepted this for repair, but here it is on my desk. 

I’ve worked on a lot of those. First thing I do is soak the top of
the article with Opticon and vacum it. This should cause the Opticon
to penetrate down into the old cement and re-constitute it. As for
replacing missing pieces, companies that supply enameling supplies
often sell jars of various colors of small glass chunks and threads
of glass. Other than that, I’ve made up small bits of polymer clay to
use. When the Opticon cures, I go over the top surface with a blue
abraisive wheel in a handpiece that is specifically designed not to
scratch stones. Stuller has them.

That will clean off the excess Opticon on the surface without
dulling the glass inlays. It’s unlikely you’ll get a perfect repair,
but you can get something that is a significant improvement.

David L. Huffman


#5
A client brought in an exquisite, very old bracelet with pietra
dura inlay all over it. A chunk has come out, plus several
individual tesserae. I could find it in my heart to wish the boss
had not accepted this for repair, but here it is on my desk. 

I’ve worked on a lot of those. First thing I do is soak the top of
the article with Opticon and vacum it. This should cause the Opticon
to penetrate down into the old cement and re-constitute it. As for
replacing missing pieces, companies that supply enameling supplies
often sell jars of various colors of small glass chunks and threads
of glass. Other than that, I’ve made up small bits of polymer clay to
use. When the Opticon cures, I go over the top surface with a blue
abraisive wheel in a handpiece that is specifically designed not to
scratch stones. Stuller has them.

That will clean off the excess Opticon on the surface without
dulling the glass inlays. It’s unlikely you’ll get a perfect repair,
but you can get something that is a significant improvement.

David L. Huffman


#6

The adhesive does not show at all from the top-- each tiny piece is
tapered, so the adhesive holds it but they are all flush on the
surface.

The adhesive is brownish, and (understandably, after more than a
century) brittle.

I need an adhesive with a very long cure time so I can place the
individual loose pieces. Is an epoxy the best choice for a piece like
this? I think there are epoxies with whatever set time one needs…

Opticon after placement sounds like a good idea, but something good
and sticky, but slow-setting, has to hold the pieces while I put them
in.

Noel Yovovich


#7

no affiliation just I need specific epoxy for the current sculpting
project and I found this to be an amazing site they will answer any
questions swiftly and if you tell them the project they can advise
on best epoxy

http://www.ganoksin.com/gnkurl/ep80l5

Teri


#8

Noel,

So it was in the pietra dura restoration I mentioned: brownish and
brittle.

Try warming some scrapings on a spoon or spatula over a candle flame
or similar; also give it the red-hot needle test. If it softens and
liquifies in the heat and smells resinous when poked with the hot
needle then it’ll be pitch or Canada balsam or similar; whether you
then choose to use a close-to-original adhesive or something else is
dependent upon the “restoration ethics” that seem warranted for the
piece in question.

Cheers
Hans Durstling
Moncton, Canada